Method and apparatus for electronic commutation



June 10, 1958 E. E. TURNER Y 2,338,706

METHOD AND APPARATUS FOR ELECTRONIC COMMUTATION Filed Feb. 18, 1954 5 Sheets-Sheet 1 INVENTOR EDWIN E. TURNER ATTORNEY E. E. TURNER METHOD AND APPARATUS FOR ELECTRONIC COMMUTATION June 10, 1958 3 Sheets-Sheet 3 Filed Feb. 18, 1954 Y R E 0 mm W m E 0 M W WM GA E w WY EB Unite 2,838,706 Patented June 10, 1958 Free METHOD AND APPARATUS FOR ELECTRONIC (IQMMUTATION Application February 18, 1954-, Serial No. 411,172

2 Claims. (Cl. 313-69) This invention relates to electronic commutation, and particularly to methods and means for controlling the behavior of electronic circuits associated with an electromagnetically rotated electron beam.

The invention provides a novel method of improving the commutation effect in a rotary beam type of electronic tube, the novel method being characterized by the step of establishing a relationship between beam width and control grid dimensioning such that in every angular position of the rotary beam there is a constant aggregate energy output from the tube, with a resultant maintenance of a constant, hiatus-free transmission effect with respect to the signals successively entering the tube, resulting in a smooth, stepless gradation in the commutating action as between successively positioned signal conducting control grids.

Otherwise stated, the invention provides a rotary beam tube having beam output control means in the form of a circular array of signal conducting electrodes with beam intercepting faces so inter-disposed as to produce a proportional energy commutating action that is completely free of sharp transitional points, the control of the electronfiow being continuously shared between one signal conducting face and the next in a gradual, hiatusfree manner and without any diminution of aggregate signal influence at any stage of the beams rotary cycle.

In the herein illustrated embodiment of the invention, it is shown as applied to a rotary beam amplifier tube of the type disclosed in the copending Knauss' Patent No. 2,721,286, issued on October 18, 1955, on application Ser. No. 42,589, filed August 5, 1948. However, it is to be understood that the invention may be embodied in a variety of devices, and utilized in any application where it is desirable to achieve substantially stepless energy commutation, with an aggregate energy flow of substantially constant magnitude at all positions along the path of commutation.

Other characteristics of the invention will become apparent from the following detailed description of the embodiment selected for illustration in the accompanying drawings wherein:

Fig. 1 is a side elevation view, partly in section, of a rotary beam tube to which the invention is applicable;

Fig. 1A is a top plan view of the tube of Fig. l on a reduced scale, showing the beam-forming means;

Fig. 2 is a bottom plan view of the tube, with certain parts omitted in order to clarify the showing of certain other parts;

Fig. 3 is a perspective view showing the method of securing he upper ends of the commutating grid wires, and also showing the cathode beam in three ditferent positions in relation to the intercepting grid components;

Fig. 4 shows a portion of the grid assembly, in enlarged diagrammatic form; and

Fig. 5 is a diagram of a utilization circuit.

The tube illustrated in Fig. 1 includes a number of es- I sential parts, and other parts facilitating practice of the invention, but not actually essential thereto. The cathode 11 is surrounded by a pair of equi-diameter cylindrical electron accelerator electrodes 12 and 13 spaced axially to provide a circumferentially uninterrupted space 14 permitting radial flow of electrons. A plurality of angularly spaced control grid wires 15 surround the accelerator electrodes 12 and 13, and a pair of equi-diameter cylindrical screen electrodes 16 and 17 surround the grid wires 15 and are spaced axially to provide a second circumferentially uninterrupted passage 18 therethrough. A cylindrical anode 19 surrounds the screen electrodes. The entire assembly is supported on top and bottom plates 21 and 22, respectively, of mica or the like, and enclosed in an envelope 23, suitable for evacuation. The topand bottom plates are attached to opposite axial ends of the anode 19. The screen electrodes 16 and 17 are mounted on the inner sides of the top and bottom plates 21 and 22, respectively, concentric with the anode. Two circular insulating plates 24 and 25, of mica or the like, having like diameters less than the inner diameter of the screen electrodes but greater than the outer diameter of the accelerator electrodes, are mounted concentrically on the inner sides of the top and bottom plates 21 and 22, respectively, spaced therefrom by spacers 26 suitably distributed. The top and bottom accelerator electrodes 12 and 13 are mounted on these inner plates 24 and 2Z5,

respectively.

Rings 27 and 28, of a rigid non-conductive material, such as a ceramic, are mounted on the outside of the accelerator electrodes 12 and 13, respectively. T he inner diameter of each ring is such that it fits snugly on the accelerator electrode cylinder. Each ring is of substantial thickness in the axial direction, for example, about oneeighth inch, and is provided with a plurality of axially directed V-shaped grooves 30 (Fig. 3) equally spaced around the outer circumference thereof. The grid wires 15 are tightly stretched between these two rings 27 and 28, each wire being fastened at each end in a groove 30. The grooves are conveniently V-cut at an angle of 60 degrees.

The grid wires 15 are, in effect, the terminal electrodes of their associated lead wires 48, with each lead wire 48 terminating in a series of six of such grid wires 15 fanning out therefrom and being received in the above-described grooves 30. In the illustrated embodiment there are 48 lead wires; hence the number of grid wires is 48 times six, or 288, with the grid wire spacing, or pitch, being 360/288, or 1.25 degrees, between grid wire centers.

As indicated in Fig. 4, the cathode beam width is adjusted to coincide with an aggregate of six pitch distances which, in the installation illustrated, results in a beam width of six times 1.25 degrees, or 7 /2 degrees. The objective is to produce a grid-beam relationship such that when the beam bears evenly between two feed wires 48 (position A of Fig. 4) the electron stream control will be equally divided between the two feed wires so that each will have equal effect upon one-half the electron beam. Stated another way, the commutation between grids 45g is proportional, that is to say if the beam bears wholly on one grida grid 48g consisting of the six wires 15 fanning out from a single feed wire id-the grid thus spanned will have complete and exclusive control of the beam, for that instant, and adjacent grids on either side thereof will have no eflect whatever. (This is illustrated at position B, Fig. 4.) At the next instant thereafter the control will be apportioned between two grids in the ratio of five to one, withthe next succeeding grid exerting a one-sixth commutation effect as soon as its first grid wire 15 is spanned. The proportional effect of said succeeding grid will progressively increase to onethird, one-half, two-thirds (see position C, Fig. 4) fivesixths, and thence to exclusive control, after which it will recede progressively through five-sixths control, then twothirds, one-half, one-third, one-sixth, and eventually to complete loss of any proportion of control. In each of such progressive stages, however, the aggregate control effect of the two participating grids is constant, in obedience to the formula:

wherein E represents the total energy pick-up of the rotating electron beam, and I1 and n represent the number of grid wires intercepted on successive grids, at any given instant. The value E will remain constant in all possible positions of the beam.

The type of system indicated in Fig. 5 is most effective when the grid-beam relationship is as described above. This is due to the fact that such a system employs preformed searching sound beams which intersect in space at the half power points. It is therefore desirable that the commutation pattern of the commutator tube intersect at the half-power points, or on a voltage basis on f the 6 db points, in order to achieve stepless, harmonic commutation from one sound beam to the next. Moreover, the erfect is to derive additional beam signals, by interpolation, at intermediate bearing points half-way between each successive pair of normal bearing points, corresponding to the positions when the tube beam is bearing equally upon any two successive grids 48g.

Instead of constructing each grid 48g of six parallel Wires 15, the grids can embody any desired larger number of wires equally spaced along the 7 /2 degree arcuate length encompassed by each grid. Alternatively, each grid can be constructed of wire mesh, or it can approach the form of a solid screen or plate of 7 /2 degree arcuate span, or some shorter arcuate span if the total number of lead wires exceeds the forty-eight shown in the assumed embodiment, it being understood that the formula for grid span, in degrees, is 360/N, with N designating the number of grids-the term grid" embracing all those wires or other conducting element (screen or plate) serving as the terminal electrode for an individual lead wire 48.

The cathode 11 of the illustrated embodiment is coated with emissive material, with the active area being the portion disposed between the electrically conductive shields 31 and 32 which cover the end portions of the cathode, said end portions being received in the abovedescribed supporting plates 24 and 25 which hold the cathode aligned with the tube axis. The shields 31 and 32 block electron emission from their respective end sections of the cathode. The cathode is preferably indirectly heated, in a well-known manner (not shown).

While the mechanical construction of the illustrated tube is not, per se, of any significance in understanding the subject invention, a brief description thereof may be helpful in explaining the illustrated application of the invention. The tube assembly includes outer rods 33 and 38 fastened, as by welding, to the anode 19 at diametrically opposed points; another pair of rods 3% and 37 similarly fastened to the lower screen electrode 17; and a third pair of electrically conductive rods 35 and 36 similarly fastened to the lower accelerator electrode 13. A stabilizing rod 39 is fastened between the innermost two rods 35 and 36, at points a substantial distance from the electrode assembly. While the various pairs of rods that are fastened to the different electrodes are shown lying on the same diameter in Fig. 1, it will be appreciated that they can, and they preferably will, lie on different diameters. The upper screen electrode to is provided with an electrical connection lug 41 extending through the top outer supporting plate 21, and is electrically connected to the lower screen electrode 1? by a wire 42 connected between this lug and one of the rods 34 connected to the lower electrode. The upper accelerator electrode 12 is provided with an electrical connection lug 53 extending through both the inner and the outer top supporting plates 24 and 4. 21, respectively, and is connected to the lower accelerator electrode 13 by a wire 44 connected between this lug and one of the rods 36 connected to the lower accelerator electrodes. The cathode is provided with a pair of connecting wires 45 and 46 to the heater (not shown) and a single connecting wire 47 to the heated element.

The envelope 23 is made preferably of glass in two parts, of which the upper 51 is the larger and contains the tube element assembly and the supporting and connecting conductors. The lower portion 52 completes the envelope, and is provided with an extension 53 through which the envelope is exhausted, and which is then sealed off. Each envelope portion is thickened at the rim 54, 55 of its mouth and it is at these thickened rims that the two portions are sealed together to form the completed envelope. When the rims are sealed together, they form a thickened annulus in which all the electrical connection terminals of the tube are sealed. As shown in Fig. 2, the terminals 56 all project radially from the thick-- ened annulus. Each terminal 56 is an elongated rigid rod which projects radially into the envelope 23 a sufiicient distance to meet the axially disposed conductor to which it is to be connected, as shown at 57. The terminal rods 5'6 are thus each disposed at right angles to the wires 48, 4'7, 46 and 45, and the supporting conductors 33 to 38, inclusive, to which they are connected. Being rigid, the terminal rods 56 that are connected to the wires 45 to 48, inclusive, serve to hold those wires taut while the remaining terminal rods serve to support the electrode assembly in the envelope.

The electrons emitted by the cathode 11 are formed into a pair of oppositely directed beams 61 and 62, by suitable magnetic means having two opposite poles N and S, disposed closely outside the tube envelope on diametrically opposite sides of the electrode assembly. The magnetic poles are rotated about the tube axis to operate the tube as a commutator. The rotatable magnetic field can be provided in any convenient manner. In the illustrated embodiment, a tetrapolar electromagnetic resolver 64, shown in Fig. 1A, having a coil 65, 66, 67, and 68 for each of its four poles, provides the rotatable magnetic field when the four coils are energized by sinusoidal voltages in phase quadrature, as is Well known. The poles of the resolver are uniformly distributed about the circumference of the tube 19. Although not in any sense a part of the subject invention, the particular construction shown operates to tilt the beams 61 and 2 with respect to the tube axis, so that one beam 61 passes through the annular passages 14 and 1S and reaches the anode 19, while the oppositely directed beam 62 is interrupted by the material of the lower accelerator electrode 13. To this end the cathode 11 is disposed partially below the general plane of the first or inner annular passage 14 and completely below the general plane of the second or outer annular passage 18. The outer passage 18 is to this end axially displaced toward the top of the tube 10 with respect to the inner passage .l4. An electromagnetic field for tilting the beam toward parallelism with the tube axis is provided by a solenoidal coil 69, which may be wound closely on the envelope 23 near the electrode assembly as shown, or disposed in any other convenient location. This coil provides a magnetic field parallel to the tube axis when energized with direct current. The feature of tilting the beam is described and claimed in United States Patent No. 2,654,641 granted September 29, 1953.

During operation of the tube, the beam 61 which is employed for commutation sweeps by successive grid wires 15, as above described. The cross-sectional shape of the beam is generally rectangular, as indicated in Pig. 4, due to the rectangular shape of the cathode 11 when viewed along the beam axis. The focussing magnetic field does not change this shape appreciably. Further, the annular apertures 14 and L; are both of sufficient width so that the beam can pass through substantially without any of the beam electrons impinging upon the electrode metal. This contributes to quiet operation of the tube. As indicated at 63 in Fig. 1, a virtual cathode is formed on the outer side of the accelerator electrode aperture 14. The electronic action responsible for formation of this virtual cathode is explained in detail in the above-identified copending application, Serial No. 42,589, filed August 5, 1948. It is in no respect essential to the invention herein claimed, and is shown only because it is inherent in the operation of the specific tube illustrated in Fig. 1. As heretofore noted, the tube construction may be varied as desired, so long as the electron beam commutation follows the principles indicated as the essence of the subject invention.

In the illustrated embodimentand, again, this is not essential but merely illustrative-the average velocity of the electrons in the virtual cathode 63 is such that the virtual cathode is at a potential level of approximately one volt with respect to the actual or real cathode. The grid wires 15 are placed very close to the virtual cathode and operated at the same potential level. The anode 19 is placed a suitable distance away and operated at a potential level of about 300 volts. There is accordingly at all times a flow of electrons from the virtual cathode to the anode. The screen electrodes 16 and 17 are maintained at the potential of the real cathode 11. The plate current changes rapidly with small change in grid potential about a median level of the order of one volt with respect to the cathode. Above this region, the plate current becomes substantially constant with increasing grid potential, until the grid potential is increased to a value where the grid begins to draw current. Above this value of grid potential, the plate current is diminished by the amount taken by the grid.

In the utilization circuit illustrated in Fig. 5, the cathode lead 47 is grounded at 71. A battery 72 furnishes about 20 volts positive bias to the accelerator electrodes 12 and 13. This battery is connected at its positive terminal to the accelerator grid connection lead 36 and at its negative terminal to the cathode, or ground 71. A by-pass capacitor 73 is connected across the battery 72. The screen electrodes 16 and 17 are connected to ground via their common connecting lead 34. Signals which are to be commutated are provided to the grid wires 15 'by individual signal generators G1, G2, G3, each of which is connected at one side to a separate coupling capacitor 75, 76, 77, respectively, and at the other side to ground. As heretofore explained, 48 separate signals can be commutated with the tube that is illustrated, and it is to be understood that the three signal generators that are shown are symbolic of all 48 such devices. The signals themselves can come from any source as, for example, an array of sound transducers or antennae wherein each individual signal represents a different member or a different directivity of the array. A system of underwater sound transducers wherein the present invention may be employed to advantage is described and claimed in the copending Rich application, Serial No. 14,017, filed March 10, 1948. A signal coupling resistor 81, 82, 83 is connected from the grid lead 48 of each signal generator G1, G2, or G3, respectively, to a common junction 84 for all the coupling resistors. A grid bias battery 85 is connected between the common junction and ground 71, the positive terminal of the battery being connected to the common junction. The battery 85 furnishes the grid wires with a small bias of about one volt positive with respect to the cathode 11. The anode 19 is provided with about 300 volts positive unidirectional potential with respect to the cathode by a battery 88 through a load resistor 89. The battery 88 is connected to ground 71 at its negative terminal and at its positive terminal to the resistor 89, which is in turn connected to the anode lead 33. A by-pass capacitor 91 is connected across the battery 88. The commutated signal is coupled to succeeding stages via a coupling capacitor 92.

The plate-to-cathode resistance of the tube is of the order of several megohms. The plate circuit load resistor 89 may preferably be any value between 10,000 ohms and one megohm, although other values may be used if desired. It will be appreciated that the batteries 72, 85, and 88 are symbolic of any and all the usual and well-known systems for providing tube electrode potentials. The utilization circuit of Fig. 5 provides any desired value of gain from 0.1 to 5.0, depending on the circuit constants and electrode potentials that are chosen.

When the invention is embodied in a rotary beam tube of more conventional design, that is, a tube in which there are two effective beams, both normal to the cathode axis and both being free to travel in two diametrically opposed directions, without obstruction, until intercepted by a cylindrical anode, concentric there with, at two diametrically opposed areas on the anode surface, the grid construction and spacing can remain as above described except that diametrically opposed lead wires 48 will preferably be interconnected externally so that the thus electrically paired wires may simultaneously exert equal control efifects upon the respective beams. Each beam will have a width corresponding to the grid width, to conform to the principles of operation herein developed. Other tube designs, however, can readily be utilized as vehicles for practice of the invention, as the invention is not limited to the particular details of construction, materials and processes described, and many equivalents will suggest themselves to those skilled in the art. It is accordingly desired that the appended claims be given a broad interpretation commensurate with the scope of the invention within the art.

What is claimed is:

1. An electronic commutation device for use in a rotary beam tube, said device comprising a plurality of signal transfer elements in circumferentially discrete circular array, and means for rotating an electron beam past said elements successively, each signal transfer element' having a beam intercepting face constituted by a plurality of closely positioned energy exchange points all of which are adapted to be embraced within the beam area, in one angular position thereof, to distribute the signal transfer action evenly therebetween.

2. An electronic commutator tube device comprising a cylindrical anode, a cathode positioned substantially on the axis of said anode, means for forming electrons from said cathode into a beam extending toward said anode, means sweeping said beam angularly about said cathode and a plurality of generally axially directed arrays of control grid wires arranged about said cathode in a circle concentric with said cathode and separated by a space less than the width of the electron beam.

References Cited in the file of this patent UNITED STATES PATENTS 2,293,368 Stuart Aug. 18, 1942 2,345,115 Hall Mar. 28, 1944 2,390,884 Jansky Dec. 11, 1945 2,513,947 Levy July 4, 1950 2,645,741 Westervelt et al. July 14, 1953 2,652,514 Davison Sept. 15, 1953 2,701,319 Coleman Feb. 1, 1955 

